Broad Absorption Line Outflows Research Articles

On the origins of C iv absorption profile diversity in broad absorption line quasars

There is a large diversity in the C IV broad absorption line (BAL) profile among BAL quasars (BALQs). We quantify this diversity by exploring the distribution of the C IV BAL properties, FWHM, maximum depth of absorption and its velocity shift ($v_{\rm md}$), using the SDSS DR7 quasar catalogue. We find the following: (i) Although the median C IV BAL profile in the quasar rest-frame becomes broader and shallower as the UV continuum slope ($\alpha_{\rm UV}$ at 1700-3000 A) gets bluer, the median individual profile in the absorber rest-frame remains identical, and is narrow (FWHM = 3500 km/s) and deep. Only 4 per cent of BALs have FWHM > 10,000 km/s. (ii) As the He II emission equivalent-width (EW) decreases, the distributions of FWHM and $v_{\rm md}$ extend to larger values, and the median maximum depth increases. These trends are consistent with theoretical models in which softer ionizing continua reduce overionization, and allow radiative acceleration of faster BAL outflows. (iii) As $\alpha_{\rm UV}$ becomes bluer, the distribution of $v_{\rm md}$ extends to larger values. This trend may imply faster outflows at higher latitudes above the accretion disc plane. (iv) For non-BALQs, the C IV emission line decreases with decreasing He II EW, and becomes more asymmetric and blueshifted. This suggests an increasing relative contribution of emission from the BAL outflow to the C IV emission line as the ionizing spectral energy distribution (SED) gets softer, which is consistent with the increasing fraction of BALQs as the ionizing SED gets softer.

Radiation pressure confinement – IV. Application to broad absorption line outflows

A fraction of quasars present broad absorption lines, produced by outflowing gas with typical velocities of 3000 - 10,000 km/s. If the outflowing gas fills a significant fraction of the volume where it resides, then it will be highly ionized by the quasar due to its low density, and will not produce the observed UV absorption. The suggestion that the outflow is shielded from the ionizing radiation was excluded by recent observations. The remaining solution is a dense outflow with a filling factor $f<10^{-3}$. What produces such a small $f$? Here we point out that radiation pressure confinement (RPC) inevitably leads to gas compression and the formation of dense thin gas sheets/filaments, with a large gradient in density and ionization along the line of sight. The total column of ionized dustless gas is a few times $10^{22}$ cm$^{-2}$, consistent with the observed X-ray absorption and detectable P V absorption. The predicted maximal columns of various ions show a small dependence on the system parameters, and can be used to test the validity of RPC as a solution for the overionization problem. The ionization structure of the outflow implies that if the outflow is radiatively driven, then broad absorption line quasars should have $L/L_{\rm Edd} \gtrsim 0.1$.

Extragalactic jets of broad absorption line (BAL) quasars

AbstractFast outflows of the ionized plasma, probably lunched in proximity of Supermassive Black Hole, are responsible for blue-shifted Broad Absorption Lines (BALs) in quasar spectrum. Outflows together with powerful jets produced in AGN are important feedback processes. Therefore, understanding physics behind BAL outflows might be a key to comprehend Galaxy Evolution as a whole. Discovery of the existence of radio-loud BAL quasars gave us another opportunity to study the BAL phenomenon, this time on the ground on radio emission. The radio emission is an additional tool to understand the BAL quasars, their orientation and age, by the VLBI imaging (detection of radio jets and their direction, size determination), the radio-loudness parameter distribution and variability study.

Variability in Low Ionization Broad Absorption Line outflows

We present results of our time variability studies of Mg II and Al III absorption lines in a sample of 22 Low Ionization Broad Absorption Line QSOs (LoBAL QSOs) at 0.2 <= zem <= 2.1 using the 2m telescope at IUCAA Girawali Observatory over a time-scale of 10 days to 7.69 years in the QSO's rest frame. Spectra are analysed in conjunction with photometric light curves from Catalina Real-Time Transient Survey. Long time-scale (i.e >= 1 year) absorption line variability is seen in 8 cases (36% systems) while only 4 of them (i.e 18% systems) show variability over short time-scales (i.e < 1 year). We notice a tendency of highly variable LoBAL QSOs to have high ejection velocity, low equivalent width and low redshift. The detection rate of variability in LoBAL QSOs showing Fe fine-structure lines (FeLoBAL QSOs) is less than that seen in non-Fe LoBAL QSOs. Absorption line variability is more frequently detected in QSOs having continuum dominated by Fe emission lines compared to rest of the QSOs. Confirming these trends with a bigger sample will give vital clues for understanding the physical distinction between different BAL QSO sub-classes. We correlate the absorption line variability with various parameters derived from continuum light curves and find no clear correlation between continuum flux and absorption line variabilities. However, sources with large absorption line variability also show large variability in their light curves. We also see appearance/disappearance of absorption components in 2 cases and clear indications for profile variations in 4 cases. The observed variability can be best explained by a combination of process driven by continuum variations and clouds transiting across the line of sight.

FeLoBAL Outflow Variability Constraints from Multi-Year Observations

AbstractThe physical properties and dynamical behavior of Broad Absorption Line (BAL) outflows are crucial themes in understanding the connections between galactic centers and their hosts. FeLoBALs (identified with the presence of low-ionization Fe II BALs) are a peculiar class of quasar outflows that constitute ~ 1% of the BAL population. With their large column densities and apparent outflow kinetic luminosities, FeLoBALs appear to be exceptionally powerful and are strong candidates for feedback in galaxy evolution. We conducted variability studies of 12 FeLoBAL quasars with emission redshifts 0.69 ≤ z ≤ 1.93, spanning both weekly and multi-year timescales in the quasar's rest frame. We detected absorption-line variability from low-ionization species (Fe II, Mg II) in four of our objects, with which we established a representative upper limit for the distance of the absorber from the supermassive black hole (SMBH) to be ~20 parsecs. Our goals are to understand the mechanisms producing the variability (e.g. ionization changes or gas traversing our line of sight) and place new constraints on the locations, structure, and kinetic energies of the outflows.

MISALIGNMENT OF THE JET AND THE NORMAL TO THE DUSTY TORUS IN THE BROAD ABSORPTION LINE QSO FIRST J155633.8+351758

We performed VLBA observations of the Broad Absorption Line Quasar FIRST\,J155633.8+351758, "the first radio loud BALQSO". Our observations at 15.3 GHz partially resolved a secondary component at positional angle (PA) $\approx 35^{\circ}$. We combine this determination of the radio jet projection on the sky plane, with the constraint that the jet is viewed within $14.3^{\circ}$ of the line of sight (as implied by the high variability brightness temperature) and with the position angle (PA) of the optical/UV continuum polarization in order to study the quasar geometry. Within the context of the standard model, the data indicates a "dusty torus" (scattering surface) with a symmetry axis tilted relative to the accretion disk normal and a polar broad absorption line outflow aligned with the accretion disk normal. We compare this geometry to that indicated by the higher resolution radio data, brightness temperature and optical/UV continuum polarization PA of a similar high optical polarization BALQSO, Mrk\,231. A qualitatively similar geometry is found in these two polar BALQSOs; the continuum polarization is determined primarily by the tilt of the dusty torus.

THE SURPRISING ABSENCE OF ABSORPTION IN THE FAR-ULTRAVIOLET SPECTRUM OF Mrk 231

Mrk 231, the nearest (z = 0.0422) quasar, hosts both a galactic-scale wind and a nuclear-scale iron low-ionization broad absorption line (FeLoBAL) outflow. We recently obtained a far-ultraviolet (FUV) spectrum of this object covering ~1150 - 1470 A with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. This spectrum is highly peculiar, highlighted by the presence of faint (~< 2% of predictions based on H-alpha), broad (>~ 10,000 km/s at the base), and highly blueshifted (centroid at ~ -3500 km/s) Ly-alpha emission. The FUV continuum emission is slightly declining at shorter wavelengths (consistent with F_lambda ~ lambda^1.7) and does not show the presence of any obvious photospheric or wind stellar features. Surprisingly, the FUV spectrum also does not show any unambiguous broad absorption features. It thus appears to be dominated by the AGN, rather than hot stars, and virtually unfiltered by the dusty FeLoBAL screen. The observed Ly-alpha emission is best explained if it is produced in the outflowing BAL cloud system, while the Balmer lines arise primarily from the standard broad emission line region seen through the dusty (A_V ~ 7 mag.) broad absorption line region. Two possible geometric models are discussed in the context of these new results.

Variability in quasar broad absorption line outflows – III. What happens on the shortest time-scales?

Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution, and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in CIV 1549A BALs in our full multi-epoch sample, which covers time-scales from 0.02-8.7 yr in the quasar rest-frame. Our sample contains up to 13 epochs of data per quasar, with an average of 7 epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales <2 months. This revealed variability down to the shortest time-scales we probe (8-10 days). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Typical variability times of order ~1 year indicate crossing speeds of a few thousand km/s and radial distances near ~1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 days require crossing speeds of 17 000 - 84 000 km/s and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission line region.

The rest-frame ultraviolet properties of radio-loud broad absorption line quasars

We recently presented radio observations of a large sample of radio-loud broad absorption line (BAL) quasars from the SDSS and FIRST surveys, as well as a well matched sample of unabsorbed quasars, primarily to measure their radio spectral indices and estimate ensemble orientations. Here, we analyze the SDSS spectra of these samples and compare the rest-frame ultraviolet properties of radio-loud BAL and non-BAL quasars. Ultraviolet properties include the continuum shape, emission-line measurements of C IV, Al III, C III], Fe II, and Mg II, and BAL properties including the balnicity index (BI), absorption index (AI), and minimum and maximum outflow velocities. We find that radio-loud BAL quasars have similar ultraviolet properties compared to radio-loud non-BAL sources, though they do appear to have redder continua and stronger Fe II emission, which is consistent with what is found for radio-quiet BAL sources. No correlations exist between outflow properties and orientation (radio spectral index), suggesting that BAL winds along any line of sight are driven by the same mechanisms. There are also few correlations between spectral index and other properties. We conclude that BAL outflows occur along all lines of sight with similar strengths and velocities.

The orientation and polarization of broad absorption line quasars★

We present new spectropolarimetric observations of 8 radio-loud broad absorption line (BAL) quasars, and combine these new data with our previous spectropolarimetric atlases (of both radio-loud and radio-quiet objects) in order to investigate the polarization properties of BAL quasars as a group. The total (radio-selected) sample includes 36 (26) high-ionization and 22 (15) low-ionization BAL quasars. On average, we confirm that broad emission lines are polarized at a level similar to or less than the continuum and broad absorption troughs are more highly polarized, but we note that these properties are not true for all individual objects. Of the whole sample, 18 (31%) have high (>2%) continuum polarization, including 45% of the LoBALs and 22% of HiBALs. We identify a few correlations between polarization and other quasar properties, as well as some interesting non-correlations. In particular, continuum polarization does not correlate with radio spectral index, which suggests that the polarization is not due to a standard geometry and preferred viewing angle to BAL quasars. The polarization also does not correlate with the amount of intrinsic dust reddening, indicating that the polarization is not solely due to direct light attenuation either. Polarization does appear to depend on the minimum BAL outflow velocity, confirming the results of previous studies, and it may correlate with the maximum outflow velocity. We also find that continuum polarization anti-correlates with the polarization in the C IV broad emission and broad absorption. These results suggest that the polarization of BAL quasars cannot be described by one simple model, and that the scatterer location and geometry can vary significantly from object to object.

BAL PHOSPHORUS ABUNDANCE AND EVIDENCE FOR IMMENSE IONIC COLUMN DENSITIES IN QUASAR OUTFLOWS: VLT/X-SHOOTER OBSERVATIONS OF QUASAR SDSS J1512+1119

We present spectroscopic analysis of the broad absorption line outflow in quasar SDSS J1512+1119. In particular, we focus our attention on a kinematic component in which we identify PV and SIV/SIV* absorption troughs. The shape of the unblended phosphorus doublet troughs and the three SIV/SIV* troughs allow us to obtain reliable column density measurements for these two ions. Photoionization modelling using these column densities and those of HeI* constrain the abundance of phosphorus to the range of 0.5-4 times the solar value. The total column density, ionization parameter and metalicity inferred from the PV and SIV column densities leads to large optical depth values for the common transition observed in BAL outflows. We show that the true CIV optical depth, is about 1000 times greater in the core of the absorption profile than the value deduced from its apparent optical depth.

BAL OUTFLOW CONTRIBUTION TO AGN FEEDBACK: FREQUENCY OF S IV OUTFLOWS IN THE SDSS

We present a study of Broad Absorption Line (BAL) quasar outflows that show S IV ?1063 and S IV* ?1073 troughs. The fractional abundance of S IV and C IV peak at similar value of the ionization parameter, implying that they arise from the same physical component of the outflow. Detection of the S IV* troughs will allow us to determine the distance to this gas with higher resolution and higher signal-to-noise spectra, therefore providing the distance and energetics of the ubiquitous C IV BAL outflows. In our bright sample of 156 SDSS quasars 14% show C IV and 1.9% S IV troughs, which is consistent with a fainter magnitude sample with twice as many objects. One object in the fainter sample shows evidence of a broad S IV trough without any significant trough present from the excited state line, which implies that this outflow could be at a distance of several kpc. Given the fractions of C IV and S IV, we establish firm limits on the global covering factor on S IV that ranges from 2.8% to 21% (allowing for the k-correction). Comparison of the expected optical depth for these ions with their detected percentage suggests that these species arise from common outflows with a covering factor closer to the latter.

Erratum: Spectropolarimetry of PKS 0040−005 and the orientation of broad absorption line quasars

We have used the Very Large Telescope (VLT) to obtain spectropolarimetry of the radio-loud, double-lobed broad absorption line (BAL) quasar PKS 0040−005. We find that the optical continuum of PKS 0040−005 is intrinsically polarized at 0.7 per cent with an electric vector position angle nearly parallel to that of the large-scale radio axis. This result is naturally explained in terms of an equatorial scattering region seen at a small inclination, building a strong case that the BAL outflow is not equatorial. In conjunction with other recent results concerning BAL quasars, the era of simply characterizing these sources as ‘edge-on’ is over.

THE TRANSITION FROM “NORMAL” TO “BROAD ABSORPTION LINE QUASAR” OF TON 34

We report the emergence of a high velocity, broad absorption line outflow in the luminous quasar Ton 34, at z=1.928. The outflow is detected through an ultraviolet CIV broad absorption line, in a spectrum obtained in January 2006 by the Sloan Digital Sky Survey. No absorption trough was present in two different spectra acquired in 1981 at Las Campanas and Palomar observatories, indicating the emergence of the outflow in less than ~8 yr (rest-frame). The absorption line spans a velocity range from ~5,000-26,000 km s-1}, and resembles typical troughs found in Broad Absorption Line quasars (BALQSOs). We measure a balnicity index >600 (tough this value might be an underestimation due to a conservativeplacing of the continuum). The absorption trough is likely saturated, with the absorbing gas covering ~25% of the emitting region. We explore different scenarios for the emergence of this outflow, and find an existing wind moving across our line of sight to the source as the most likely explanation. This indicates that high velocity outflows (producing broad absorption troughs in BALQSOs) might be ubiquitous in quasars, yet only become observable when the wind accidentally crosses our line vision to the central source.

Variability and the X-ray/UV ratio of active galactic nuclei

The observed relation between the X-ray radiation from AGNs, originating in the corona, and the optical/UV radiation from the disk is usually described by the anticorrelation between the UV to X-ray slope alpha_ox and the UV luminosity. Many factors can affect this relation, including: enhanced X-ray emission associated with the jets of radio-loud AGNs; X-ray absorption associated with the UV Broad Absorption Line (BAL) outflows; other X-ray absorption not associated with BALs; intrinsic X-ray weakness; UV and X-ray variability, and non-simultaneity of UV and X-ray observations. The separation of these effects provides information about the intrinsic alpha_ox-L_UV relation and its dispersion, constraining models of disk-corona coupling. We extract simultaneous data from the second XMM-Newton serendipitous source catalogue and the XMM-Newton Optical Monitor Serendipitous UV Source Survey Catalog, and derive the single-epoch alpha_ox indices. We use ensemble structure functions to analyse multi-epoch data. We confirm the anticorrelation of alpha_ox with L_UV, and do not find any evidence of a dependence of alpha_ox on z. The dispersion in our simultaneous data (0.12) is not significantly smaller than in previous non-simultaneous studies, suggesting that "artificial alpha_ox variability" introduced by non-simultaneity is not the main cause of dispersion. "Intrinsic alpha_ox variability", i.e., the true variability of the X-ray to optical ratio, is instead important, and accounts for ~30% of the total variance, or more. "Inter-source dispersion", due to intrinsic differences in the average alpha_ox values from source to source, is also important. The dispersion introduced by variability is mostly caused by the long timescale variations, which are expected to be driven by the optical variations.

THE EVOLUTION OF QUASAR C IV AND Si IV BROAD ABSORPTION LINES OVER MULTI-YEAR TIMESCALES

We investigate the variability of CIV 1549A broad absorption line (BAL) troughs over rest-frame time scales of up to ~7 yr in 14 quasars at redshifts z>2.1. For 9 sources at sufficiently high redshift, we also compare CIV and SiIV 1400A absorption variation. We compare shorter- and longer-term variability using spectra from up to four different epochs per source and find complex patterns of variation in the sample overall. The scatter in the change of absorption equivalent width (EW), Delta EW, increases with the time between observations. BALs do not, in general, strengthen or weaken monotonically, and variation observed over shorter (<months) time scales is not predictive of multi-year variation. We find no evidence for asymmetry in the distribution of Delta EW that would indicate that BALs form and decay on different time scales, and we constrain the typical BAL lifetime to be >~30 yr. The BAL absorption for one source, LBQS 0022+0150, has weakened and may now be classified as a mini-BAL. Another source, 1235+1453, shows evidence of variable, blue continuum emission that is relatively unabsorbed by the BAL outflow. CIV and SiIV BAL shape changes are related in at least some sources. Given their high velocities, BAL outflows apparently traverse large spatial regions and may interact with parsec-scale structures such as an obscuring torus. Assuming BAL outflows are launched from a rotating accretion disk, notable azimuthal symmetry is required in the outflow to explain the relatively small changes observed in velocity structure over times up to 7 yr.

ON THE SCATTERING ENHANCEMENT OF N V λ1240 EMISSION LINE OF QUASI-STELLAR OBJECTS

The Nv emission line of active galactic nuclei shows peculiar behavior in the line--continuum correlation, which may be indicative of an extra line component in addition to that from the normal broad emission line region. In this paper, we investigate possible contribution to the Nv emission via resonant scattering of both continuum and Ly alpha in a broad absorption line (BAL) outflow, by performing the Sobolev Monte Carlo simulations. The contribution is dependent on the covering factor, optical depth and velocity profile of the outflow, as well as the equivalent width (EW) of Ly alpha. Adopting model parameters constrained by observations, we find that the measured Nv EW in the spectra of non-BAL quasi-stellar objects (QSOs) could have been enhanced by a factor of 1.82~2.73 on average, while there is only moderate absorption of Ly alpha along the BAL outflow direction. Our model can produce a relatively narrow scattering line profile. About 80% of the total scattered flux falls within the central +-4500km/s. We find that the resonant scattering can produce a prominent polarized emission line around Nv. Both the broad excess emission and the unusually large polarized flux observed around Nv in BAL QSOs are considered as strong evidence for the scattering enhancement. Future spectropolarimetric observations and spectroscopic monitoring of luminous QSOs may offer crucial tests for this interpretation, and provide useful information on the physical and geometrical properties of QSO outflows. We argue that the scattering offers a promising and robust process for producing the peculiar behavior of Nv emission compared to the other processes proposed previously.

VLBI Detections of Parsec-Scale Nonthermal Jets in Radio-Loud Broad Absorption Line Quasars

Abstract We conducted radio detection observations at 8.4 GHz for 22 radio-loud broad absorption line (BAL) quasars, selected from the Sloan Digital Sky Survey Third Data Release, by a very-long-baseline interferometry (VLBI) technique. The VLBI instrument we used was developed by the Optically ConnecTed Array for VLBI Exploration project (OCTAVE), which is operated as a subarray of the Japanese VLBI Network. We aimed to select BAL quasars with nonthermal jets suitable for measuring their orientation angles and ages by subsequent detailed VLBI imaging studies to evaluate two controversial issues of whether BAL quasars are viewed nearly edge-on, and of whether BAL quasars are in a short-lived evolutionary phase of the quasar population. We detected 20 out of 22 sources using the OCTAVE baselines, implying brightness temperatures greater than 10$^{5}$ K, which presumably come from nonthermal jets. Hence, BAL outflows and nonthermal jets can be generated simultaneously in these central engines. We also found four inverted-spectrum sources, which are interpreted as Doppler-beamed, pole-on-viewed relativistic jet sources, or young radio sources: single edge-on geometry cannot describe all BAL quasars. We discuss the implications of the OCTAVE observations for investigations for the orientation and evolutionary stage of BAL quasars.

The Impact of BAL Outflows on Cosmological Structure Formation

AbstractQuasar feedback has been invoked as a major mechanism for influencing large-scale cosmological structure. To quantify to what extent they affect the real universe, one needs to measure the mechanical energy output of quasars and assess the ability of this energy to produce the feedback. We have developed an observational/modeling program that has yielded the first reliable kinetic luminosity determinations of quasar broad absorption line (BAL) outflows, and have demonstrated that energetically they are indeed a major contributor to AGN feedback.

Variability in Quasar Broad Absorption Line Outflows

Broad absorption lines (BALs) in quasar spectra identify high-velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution (e.g., Di Matteo et al. 2005). Studying the variability in these BALs can help us understand the structure, evolution, and basic physical properties of these outflows. We are investigating BAL variability in a sample of 25 luminous quasars at 1.2 &lt; z &lt; 2.9 with multi-epoch observations that cover time scales from less than around a month to 7.7 years in the quasar rest-frame. We investigate changes in the C iv λ1549 BALs, and we see a variety of phenomena, including some BALs that either appeared or disappeared completely and other BALs that did not change at all over the whole observation period.